> That said, it is possible to write file names containing bytes that can't decode as UTF-8.

I can't believe that. Could you please give an reproducible example?

> I think LC_ALL is relevant to what the encoding of svn's output should be.

I'm sure, you mixed here two things: the file names and the output. File
names should be always convertible to a general character representation
like UTF-8. Displaying the file names with the right sign in the output is a
different issue and might depend on the used font.

If you think, LC_ALL should be relevant for the file name detection in
Subversion, could you give answers for the following questions:
- What LC_ALL-value the user should set?
- What should happen when the wrong value was set?
- What value to set for file names in different languages?